Corrosion of pipelines under cathodic protection (CP) caused by induced alternating current (AC) is highly dependent on the cathodic current density. This study uses electrical resistance probes to produce a corrosion rate map of the AC/DC current density domain, using a galvanostatic CP system subject to varying AC voltage interference levels. Two corrosion domains are recognized at high or low CP, respectively. X-ray photoelectron spectroscopy is utilized for analysis of surface oxides, being primarily magnetite and ferrous hydroxide. The results are discussed in a Pourbaix diagram context.